UV effects on photosynthesis, growth and acclimation of an estuarine diatom and cryptomonad

Ultraviolet (UV) radiation is a significant stressor in aquatic environments and can inhibit primary productivity of phytoplankton. The effects of UV depend on many factors, including phytoplankton community composition and acclimation status. Using spectrally resolved biological weighting functions (BWFs), we determined sensitivity of photosynthesis and acclimation to UV in a common estuarine diatom, Thalassiosira pseudonana (Hustedt) Hasle et Heimdal, and cryptomonad, Cryptomonas sp. Cryptomonas sp. grown under high PAR (photosynthetically active radiation) (250 μmol quanta m–2 s–1) was significantly more sensitive to photoinhibition in the UV-B part of the spectrum (280 to 320 nm) than T. pseudonana under high PAR. Growth under low irradiance (25 μmol quanta m–2 s–1) increased sensitivity of T. pseudonana. After a week-long exposure to moderate UV radiation, sensitivity of Cryptomonas sp. declined, while sensitivity of T. pseudonana did not change. Growth rates and chlorophyll a-specific absorption decreased in both species. Based on the BWFs obtained in this study, we predict 11 to 26% UV inhibition of depth-integrated primary production by these species under summer conditions in a shallow, turbid temperate estuary.